Hydraulic component library for combined forward-inverse simulation approach using Modelica -

Abstract

Inverse dynamic simulation of hydraulic drives is helpful in early design stages of a hydraulic machine to answer the question whether the drive can meet dynamic load requirements and to predict the energy consumption for required load cycles. While a forward simulation of the hydraulic drive needs an implementation of the controller which generates the control input as a function of the control error, the inverse dynamic simulation can be implemented without control. This is because the required motion is simply defined as a constraint and therefore the control error is always zero. This thesis illustrates in the literature review the techniques of equation manipulation to get the inverse dynamics. These techniques are implemented in simulators which use equation based modeling language such as Modelica. A simple forward-inverse simulation example of a hydraulic servo-drive is used in Modelica to illustrate the feasibility of these techniques on inverse simulation. After proving that the hydraulic servo-drive example can be simulated in a forward and inverse approach, this thesis proposes to amend one of the current hydraulic libraries in Modelica, openHydraulics, to become viable for inverse simulations. The thesis explains the inverse simulation problems faced with the components of the openHydraulics library after modifying them to allow inverse simulations. The thesis concludes in a hydraulic servo-drive example of a gear hobbing machine actuator where the design of this actuator is optimized using the inverse simulation technique from components of the modified library. The modified hydraulics simulator library provides the design engineers with a tool to optimize their designs and produce more efficient systems without the need to tune a controller.